A Conducting Salt-Based Amperometric for Measurement of Extracellular Lactate Accumulation in Ischemic Myocardium

In this paper, fabrication, characterization, and physiological application of a miniaturized amperometric lactate biosensor are described. The sensor is based on cross-linked lactate oxidase and tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) charge transfer complex. The sensor was developed for continuous quantitative measurement of the lactate accumulation in ischemic myocardium under severe depletion of oxygen. The sensor was evaluated in vitro at an applied potential of 0.15 V vs Ag/AgCl; it proved to combine all the performance characteristics desired for the present application, such as proper response in absence of oxygen, good operational stability, good accuracy and precision (103.5 ± 1.2%), adequate response time (t_95% = 80 s), and wide linear dynamic range up to 27 mM (r = 0.9998) in N₂-saturated solutions and at 37°C. The prepared sensors (n = 12) showed sensitivity of 380 ± 90 nA/mM, and a background current of 240 ± 50 nA. The lower limit of detection is 0.4 ± 0.15 mM with a S/N ratio equal to 3. Results obtained for direct lactate monitoring in ischemic rabbit papillary muscle under no-flow conditions and PO₂ <6 mm Hg are presented.